A common technique for storing gases is via a liquefaction process where the gas is compressed and cooled from a gas phase into a liquid phase. For example, hydrogen gas liquefies at 20 K at atmospheric pressure, and approximately 70 g/L of the hydrogen gas can be stored in the liquid phase. However, the liquefaction process is very energy intensive and the liquid gas needs to be maintained at the lower temperature requiring specially designed insulated containers and very careful handling.
Another common technique for storing gases is to compress the gas into a suitable vessel. For example, a gas tank pressurized to 35 MPa can store 15 g/L of hydrogen. However, a pressurized-gas tank is heavy, cumbersome, and difficult to transport.
Gases can also be stored by chemically bonding the gas to an appropriate host material. Several types of materials have been studied as hosts, including metals, metal hydrides, glass microspheres and carbon nanotubes. However, the materials investigated so far all have low gas storage capacity. Further, high temperatures are required for releasing the gas, such as from a metal hydride, make these methods unsuitable for commercial use.
Recently, LC resonant sensors have been combined with carbon nanotube materials for utilization as gas sensors. For example, Ong, et al. IEEE Sensors Journal, 2: 82 (2002) described a gas sensor formed of a responsive multi-wall carbon nanotube/silicon dioxide composite layer deposited on a planar LC resonant circuit. The permittivity and/or conductivity of the MWNT/SiO2 composite changes with adsorption of CO2, O2, or NH3 which changes the resonant frequency of the sensor, which can be remotely monitored through a loop antenna. The sensors showed reversible response to O2 and CO2, and an irreversible response to NH3.
Hydrogen can also be stored in carbon nanostructures, such as graphite and carbon nanofibers (A. Dillon et al. Nature 386: 377 (1997), A. Chambers et al. J. Phys. Chem. B 102: 3378 (1998), and U.S. Pat. No. 5,653,951 “Storage of hydrogen in layered nanostructures” to N. Rodriguez and R. Baker). Nanostructures can be defined as atomic structures that have a spatial extent of less than a few hundred nanometers in one, two, or all three dimensions. A class of nanostructures is formed by planar networks, sometimes referred to as layered compounds. The stored hydrogen, however, is not easily released from the carbon nanostructures.
J.P. Patent Publication No. 2003225561A2, published Dec. 8, 2003 “Gas Adsorption Element” by Mitsubishi Heavy Ind. Ltd. discloses that surface of a metal foil can be coated with a carbon material. The carbon material has the capacity for hydrogen occlusion and has high thermal conductivity. The carbon material can be carbon nanotube, carbon nanofiber, or other carbon materials.
The known methods of storing gases are not convenient, require specialized equipment or handling, or high pressures or temperatures to release the trapped gasses. Accordingly, the present invention provides compositions, methods, and processes for the storing or sensing of particular gas where the gas can be easily released.